The release of oxytocin and prostaglandins appears to be the final step in the initiation of parturition. We have shown that oxytocin and possibly also other uterotonic therapeutic drugs stimulate prostaglandin biosynthesis and release in the uterus. We postulate that the marked increase in sensitivity of the parturient uterus to oxytocin may be related to the enhanced prostaglandin biosynthesis and the oxytocin-induced prostaglandin release in the term uterus. In this project, we test the validity of this hypothesis by monitoring the relationship between oxytocin sensitivity and uterine prostaglandin production in rats during the last four days of pregnancy and the effect of inhibition of prostaglandin biosynthesis on the development of oxytocin sensitivity in pregnant rats. We seek to delineate the uterotonic action and the prostaglandin-releasing action of oxytocin and the receptors involved. We also seek to elucidate the biochemical mechanism of the prostaglandin-releasing action of oxytocin. We also direct our effort to the development of a safe and effective method for the control of premature labor. We will investigate the efficacy of oxytocin antagonists in the human myometrial strips, with the specific aim to develop useful agents for the control of premature labor.